[Tee tiong huat]

May 20 (Reuters) - A helicopter carrying Iranian President Ebrahim Raisi and his foreign minister crashed on Sunday as it was crossing mountain terrain in heavy fog, an Iranian official told Reuters, and rescuers were struggling to reach the site of the incident.

Iranian Supreme Leader Ayatollah Ali Khamenei, who holds ultimate power with a final say on foreign policy and Iran's nuclear programme, sought to reassure Iranians, saying there would be no disruption to state affairs.

Iranian state media said bad weather caused the crash and was complicating rescue efforts. State news agency IRNA said Raisi was flying in a U.S.-made Bell 212 helicopter.

The official said the lives of Raisi and Foreign Minister Hossein Amirabdollahian were "at risk following the helicopter crash", which happened on the way back from a visit to the border with Azerbaijan in Iran's northwest.

"We are still hopeful but information coming from the crash site is very concerning," the official told Reuters, speaking on condition of anonymity.
State TV quoted an official as saying at least one passenger and one crew member had been in contact with rescuers.